S8) The HPA Axis & Growth Hormone Flashcards Preview

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Describe the relationship between the hypothalamus and the pituitary gland

The hypothalamus and pituitary gland form a complex functional unit that serves as the major link between the endocrine and nervous systems


Where is the pituitary gland found?


The hypothalamus and pituitary gland modulate a wide variety of processes.

Identify some

- Body growth 

- Reproduction

- Lactation

- Thyroid & adrenal gland function

- Water homeostasis


The pituitary gland consists of two distinct parts. 

What are they?


The anterior and posterior pituitary glands have distinct embryological origins.

Describe these

- Anterior pituitary gland (adenohypophysis) arises from evagination of oral ectoderm (primitive gut tissue)

- Posterior pituitary gland (neurohypophysis) originates from neuroectoderm (primitive brain tissue)


The hormones produced by nerve cells in the hypothalamus act via two distinct neurocrine pathways.

Describe these pathways

- Direct effects on distant target tissues via oxytocin and antidiuretic hormone from the posterior pituitary

- Hormones secreted exclusively into hypophyseal portal system affect endocrine cells within the anterior pituitary 


In 3 steps, outline the neuroendocrine function of the posterior pituitary gland

⇒ Oxytocin and ADH are produced by neurosecretory cells in the supraoptic and paraventricular nuclei of hypothalamus

⇒ Transported down nerve cell axons to the posterior pituitary

⇒ Stored and released from posterior pituitary into the general circulation


In four steps, describe the synthesis, transport, release and action of the hormones acting on the anterior pituitary gland

⇒ Hormones synthesised in hypothalamus

⇒ Hormones transported down axons and stored in median eminence

⇒ Hormones released into hypophyseal portal system

⇒ Hormones stimulate/inhibit target endocrine cells in the anterior pituitary gland


Describe the action of the hormones produced by the anterior pituitary gland

⇒ Endocrine cells of anterior pituitary secrete a variety of hormones into the bloodstream to act on distant target cells (endocrine function)

⇒ Anterior pituitary hormones also effect neighbouring cells (autocrine and paracrine function)


Which hormones are released from the posterior pituitary gland and what do they do?

- Oxytocin – milk let down and uterine contractions during birth

- Antidiuretic hormone – regulation of body water volume


6 tropic hormones produced in the hypothalamus and have direct effects on the release of anterior pituitary hormones.

Identify them

TRH – Thyrotropin releasing hormone / PRH

- PIH – Prolactin release-inhibiting hormone (dopamine)

- CRH – Corticotropin releasing hormone

- GnRH – Gonadotropin releasing hormone

- GHRH – Growth hormone releasing hormone

- GHIH – Growth hormone-inhibiting hormone (somatostatin)


Identify the 6 hormones produced in the anterior pituitary gland

TSH – Thyroid stimulating hormone

- ACTH – Adrenocorticotropic hormone

- LH – Luteinising hormone

- FSH – Follicle stimulating hormone

- PRL – Prolactin

- GH – Growth hormone


Summarise the relationship between the tropic hormones of the hypothalamus and the hormones produced by the adenohypophysis as well as their respective effects


Outline the hypothalamic-pituitary-adrenal axis as an example of a negative feedback system


Growth is influenced by many factors.

Identify some of these


Growth hormone is produced in the anterior pituitary.

Describe its stimulation and inhibition

Stimulation: hypothalamic GHRH

- Inhibition: hypothalamic Somatostatin 


How do growth hormones exert their effects?

- Growth-promoting effects mainly exerted indirectly via insulin-like growth factors (somatomedins)

- In response to GH cells of the liver and skeletal muscle produce and secrete IGFs 


Explain the role of GH and IGFs in bone development in childhood/teenage years as well as in adulthood

- In childhood/teenage years:

I. GH stimulates long bone growth length & width prior to epiphyseal closure (width after epiphyseal closure)

II. IGFs stimulate both bone and cartilage growth

- In adults:

I. GH & IGFs maintain muscle and bone mass and promote healing and tissue repair

II. GH & IGFs modulate metabolism and body composition


CNS regulates GH secretion via inputs into the hypothalamus affecting GHRH and somatostatin levels.

Describe some of these

- Deep sleep = surge in GH secretion

- REM sleep = ↓ GH secretion

- Exercise/stress = ↑ GH secretion

- Decreased glucose/FA = ↑ GH secretion

- Fasting = ↑ GH secretion

- Obesity = ↓ GH secretion


GH secretion is regulated by long loop and short loop negative feedback.

Describe the long loop negative feedback mechanism

Mediated by IGFs:

- Inhibit release of GHRH from hypothalamus

- Stimulate release of somatostatin from hypothalamus

- Inhibit release of GH from anterior pituitary 


GH secretion is regulated by long loop and short loop negative feedback.

Describe the short loop negative feedback mechanism

Short loop negative feedback – mediated by GH itself via stimulation of somatostatin release


What is the consequence of  growth hormone deficiency in childhood?

Pituitary dwarfism – proportionate type of dwarfism due to complete/partial deficiency 


What are the consequences of growth hormone excess?

- In childhood – gigantism (rare, often caused by pituitary adenoma)

- In adulthood – acromegaly (large hands, feet, lower jaw)


How does GH exert its effects on cells?

GH receptors activate Janus kinases (JAKs) 


There are 2 IGFs in mammals.

Describe their respective actions

- IGF1 – major growth factor in adults 

IGF2 – mainly involved in fetal growth


Binding proteins modulate the availability of IGFs.

What are the three ways in which IGFs communicate?

- Autocrine

- Paracrine

- Endocrine


IGFs act through IGF receptors (distinct from GH receptors) to modulate cell processes.

Identify four of these processes

- Hypertrophy

- Hyperplasia

- Increase in the rate of protein synthesis

- Increase in the rate of lipolysis in adipose tissue


Other hormones influence growth. Describe the growth-related actions of the following hormones:

- Insulin

- Thyroid hormones

- Androgens

- Oestrogens

- Glucocorticoids

Insulin – enhances somatic growth; interacts with IGF receptors

- Thyroid hormones – promote CNS development and enhance GH secretion

- Androgens – accelerate pubertal growth spurt; increase muscle mass; promote closure of epiphyseal plates

- Oestrogens – decrease somatic growth; promote closure of epiphyseal plate

- Glucocorticoids – inhibit somatic growth